Scientists think the amount of methane emitted to the atmosphere from freshwater ecosystems will increase as the climate warms, reports Tim Radford. And that will trigger further warming.

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This highlights another mechanism by which the global carbon cycle may serve to accelerate rather than mitigate future climate change.British scientists have identified yet another twist to the threat of global warming. Any further rises in temperature are likely to accelerate the release of methane from rivers, lakes, deltas, bogs, swamps, marshlands and rice paddy fields.

Methane or natural gas is a greenhouse gas. Weight for weight, it is 34 times more potent than carbon dioxide over a century, and 86 times more powerful over 20 years.

It's not just cattle that produce methane.

Researchers have repeatedly examined the contribution of natural gas emitted by ruminant cattle to global warming.

But Gabriel Yvon-Durocher of the University of Exeter and colleagues considered something wider: the pattern of response to temperature in those natural ecosystems that are home to microbes that release methane.